Another music theory question (key of song)

[bullshark]

Is it possible to know the key of a song with just the chord progression?

Say you had the chord progression: Bm-Em-G-F#, would that be enough to know what key you're in?

I would guess the key to be Bm, but I would only be guessing...an uneducated guess at that.

[maximilians1]

that would be my guess

[satYatunes]

As far as my knowledge on music theory is concerned: yes.
Otherwise there would be no meaning of a key.

[Sascha Franck]

Is it possible to know the key of a song with just the chord progression?

Say you had the chord progression: Bm-Em-G-F#, would that be enough to know what key you're in?

I would guess the key to be Bm, but I would only be guessing...an uneducated guess at that.

It's most likely Bm indeed.
There's a few things indicating keys, the main thing in more or less traditional sounding things being the dominant chord resolving to your tonic chord - so that's the first thing to check for.
Gets noticeably easier in case 7ths are indicated/used as well. Gets a bit more tough in case many modulations, secondary dominants, alterations and chord replacements are used.
In your given example it's fairly easy though.
As there's no 7ths indicated, look out for the major chords. There's 2, G and F#. Now, which one is resolving properly into whatever (maj or min) tonic chord a 4th up? Right, F# that is. So F#-Bm would already suit Bm. Now crosscheck the rest of the chords, whether they are existing in Bm as well. And yes, they are.
There's a lot more to it (especially if some of the aforementioned things are happening), but this is the basic stuff to check out.

[robenestobenz]

You'd look for the scale which most closely matched the notes comprising all the chord in the progression.

So, here:

Bm - B D F#
Em - E G B
G - G B D
F# - F#A#C#

B C# D E F# G A#

Here, you're in B harmonic minor. Harmonic minor is the same as the natural minor save for a raised 7th (A#/Bb, here).

Sacha's way is far faster, but I'm not really that good with theory yet. So I basically cycle through the collection of notes, starting from one higher each time, looking for a pattern I recognise.

[VladimirDimitrievich]

Not all songs have a consistent key, especially with things like prog and classical. Its not that uncommon to be in a minor key and switch to the same major key.

[bullshark]

Thanks guys. Another silly question if I may... What do I do with the A#? Do I mark it at the beginning the score as part of the key signature(sorry, only took 2 years of piano, never made it to the harmonic/natural key...first thing I learn about them is reading here, didn't even know there was such thing)?

[Sascha Franck]

Really, apart from a some exceptions (modal stuff, blues, just to name two), looking for dominant 7th chords is the trick to find keys the quickest, even in modulating pieces.
This is why it's quite easier to deal with all that stuff as soon as 7ths are indicated (or played).
Of course there's a lot more to it, such as "hidden" resolutions (a dominant not resolving properly at first), secondary dominants (that may lead into believing it's a new key all of a sudden), altered and substituted chords. Stuff like that.

Let me give you a really simple example.
One of *the* most common chord progressions in both traditional and jazz would most likely be I-VI-II-V.
Now, in the key of C major, using only chords from C major that would be Cmaj7-Amin7-Dmin7-G7.
Quite easy to analyze given the previously described approach. You'd see the G7 and the following Cmaj7 (when played in a cycle) and could then confirm that both Amin7 and Dmin7 would suit the Cmaj "criterias".
Alright, now, all of a sudden, you may find a progression going Cmaj7-A7-Dmin7-G7. What the heck is up with the A7? Are we in the key of Dmin or something? The answer is no. It's just some "intermediate" (secondary) dominant to have some more guide tones resolving properly into the Dmin chord (the C# used in A7 will nicely resolve to D).
The same could again be applied to the D chord, so it could become a D7 as well, our progression looking like Cmaj7-A7-D7-G7 now. I'd still say the entire progression is in C (and it usually feels like as well), but things are certainly starting to get blurried.

And no, that's not even remotely it. If you start using alterations, it's getting really tough.
Alterations: one or more of the socalled "option/tension" notes are raised or lowered by one halfstep, with the most drastic example being that everything but the most important chord notes (root, third and seventh) of a chord will be altered. This is usually applied on dominant chords, to create even more tension before resolving into the tonic chord.
For instance, our G7, which, in the key of C, would usually offer the extensions 9 and 13, could suddenly become a G7/b9/b13. Or even #9. Or, even more drastic, G7b5.
And while none of these altered option notes would be in the key of C major anymore, the entire progression still would.

Oh yeah, it gets even more wild. As soon as certain alterations are applied to a given chord, there's some substitutions that could kick in. Very common in classical music already, where, say, a dominant chord for a minor scale could contain a b9. Now, when you replace the root (which usually will sound automatically in your head) with the b9 (in our case, G7 = G/B/D/F would become Ab/B/D/F), you have a diminished chord, which can feature each of it's notes as the root. So Abdim7, Bdim7, Ddim7 and Fdim7 would all qualify as dominants leading to C in our progression (the most common one probably being Bdim7, as the root would nicely resolve up a halftone to C).

No, that's still not the end of it! Especially in jazzy stuff, as soon as the 5th of a dominant chord is lowered by a halftone, the entire freaking dominant chord can be replaced by a dominant chord a tritone away.
In our example, if the 5th in the G7 (G/B/D/F) would be lowered (so it'd be G/B/Db/F) the entire resulting G7/b5 chord could be played as a Db/7/#11 as well - it's only the root that's changing, otherwise it'd contain the very same notes (Db/F/G/B).
Now, if we did that to both the A chord (which, see previous example, could be played as a dominant chord) and the G chord, our progression could even look like Cmaj7-Eb7/#11-Dmin7-Db7/#11. And yes, it'd *still* sound "c major-ish".

If you're interested, I'd gladly post an audio example of these things.

Regards
Sascha

[Sascha Franck]

Thanks guys. Another silly question if I may... What do I do with the A#? Do I mark it at the beginning the score as part of the key signature(sorry, only took 2 years of piano, never made it to the harmonic/natural key...first thing I learn about them is reading here, didn't even know there was such thing)?

No, it's not marked. B minor comes with the same signature as D major (two sharps, one for the F and one for the C that is). The A# usually is only used on the dominant chord (F# in that case) anyways.

[bullshark]

You should write a book (or maybe you already did?) about music theory Sascha.

I guessed the key by looking at the sharp notes within the chords, then listening to what I was playing I guessed it had a "minor feel" to it so I dismissed D as possible key...but then I was stuck with an A# that I didn't know what to do with...

So you see, it will take me a while to digest all the info posted above, but I am gratefull for it.

[robenestobenz]

Great post Sascha, thanks for that.

[Sascha Franck]

You should write a book (or maybe you already did?) about music theory Sascha.

Hah! Don't remind me... I am indeed writing on something. Such as a "guitar handbook" or whatever it could be called. Nothing like your usual "1200 barré chords" or "splashy licks for everybody", but rather examining a few basic principles (both it terms of technique and theory) more or less thoroughly. I am 100% believing in certain musical knowledge to also improve your instrument skills drastically (very simple example: A Cmaj chord also makes up for a great Amin7/9 if played over an A bassnote, so why learn both? - as said, that's totally simplified), and that's the main aspect I'll be trying to cover.
Unfortunately, as of lately, my efforts to continue writing have been pretty much slowed down, but I hope to finish things somewhen in 2007. Expect some excerpts to be translated into english and posted for crosschecking at KVR at some time...

And regarding the A# in the key of Bm, yes, it is admittedly confusing. As a rule of thumb, one could simply remember that resolving dominant chords (those moving up a fourth to the tonic) usually require a major third. And that's all the difference between D major and B minor (which, theoretically, are parallels, thus identical), on the dominant to Bm, the A is sharpened.

Anyways, especially in not-so-classical music, all these things are taken less literally.
Fwiw, in the very progression you're dealing with, try replacing the F# with a Cmaj7 for a try. Depending on the style, it might fit fine. And while there *could* be some theoretical explanation - such as the dominant being replaced by a tritone (see previous post for details) and then some "modal interchange" being applied (the replacment chord changing from 7 to maj7) - you may already see that this would require quite a stretch to be explained halfway properly.
Sometimes it's really just easier to experiment and remember what sounds nice, instead of going for whatever theoretical explanation.

[bullshark]

How do you notate the "picking action" and variation when you write a part for a guitar player? As example: The chord progression I wrote above
If you can get past the inane playing (I'm not a guitar player, just bought a guitar last week...), you'll notice it doesn't go straight to the Bm after the Em or after the F#. Can it be noted in the score somewhat?

[Sascha Franck]

You can surely notate that.
But, on things such as that, I wouldn't notate much at all. Chord symbols, a general note such as "8th note strumming" and probably some accents written down should do the job already.

I don't understand your question completely though. What do you mean with "doesn't go straight to the Bm after the Em or after the F#"?

[bullshark]

Sorry, I don't know how to explain it better in English (I'm French, and sometime language is a barrier), that's why I posted an mp3...

I'll try to post pic of the chords to maybe explain better what I mean.